The usefulness of air refueling became apparent to the military almost as soon as they started using aircraft. The main advantage of air refueling is obvious: it enables aircraft to stay airborne longer. Since most aircraft are incapable of taking off with maximum fuel and full payload, without in-flight refueling there is always a balance to be struck between range, payload, and fuel. Air refueling is more than just a range stretcher: it allows one to carry out missions with a smaller number of sorties, or alternatively, fewer aircraft.
Currently, two major systems are used in mid-air refueling. One is the "flying boom" method in which the tanker has a tail boom equipped with aerodynamic control surfaces, which are commanded by the boom operator. The operator, who is located at the rear section of the tanker aircraft, utilizes a steering device to guide the boom into a hatch or receptacle in the receiving aircraft's upper structure.
The second common method is the hose-and-drogue system, in which a drogue attached to the fuel hose is extended from the refueling aircraft's belly or wings. The receiver aircraft is equipped with a fixed or retractable probe. In the latter method the receiving aircraft's pilot flies the aircraft "into" the drogue.
The advantages of the hose/drogue system are the following: (a) up to three receivers can take fuel simultaneously; (b) if one hose/drogue unit (HDU) becomes unserviceable, the tanker still can offload its fuel; (c) the HDU is inherently safer than the heavy, rigid boom, which is restricted in its movements; (d) it is easier to install on non-purpose-built aircraft; and (e) it is compatible with most receivers, e.g., fixed wings, as well as rotorcraft.
There are, however, two disadvantages to the hose and drogue system: it has lower fuel transfer rates than the boom system, and the drogue is uncontrollable and is susceptible to winds and gusts. In bad weather conditions and particularly in low level refueling situations the hookup process is very difficult and demands excessive receiving aircraft pilot maneuvers. Since the aircraft &o be refueled is likely to be already low on fuel, excessive maneuvering may result in the necessity to abandon the aircraft.
U.S. Pat. No. 4,763,861 to Newman, for "Microwave Rendezvous System for Aerial Refueling," relates to a microwave rendezvous system for use on a tanker aircraft for aerial refueling of a receiver aircraft. The system comprises a microwave transmitter signaling directional data towards the receiver aircraft, providing a larger rendezvous envelope in space between the tanker and receiver aircraft, and thereby requiring less tedious navigation and attention during a refueling operation.
U.S. Pat. No. 4,763,125 to Newman, for "Light Array for Providing Passive Rendezvous Guidance between Closing Aircraft Spacecraft and the Like," relates to a light array disposed along the ventral centerline of a lead aircraft to provide passive rendezvous guidance to a closing aircraft.
U.S. Pat. No. 4,633,376 to Newman, for "Advanced Fuel Receptacle Lighting System for Aerial Refueling," relates to a lighting system mounted on a tanker aircraft for enhancing a boom operator's visual view of a fuel receptacle area on the receiver aircraft during nighttime operations.
U.S. Pats. Nos. 4,519,560 and 4,231,536 to Ishimitsu et al. both relate to a ruddevator assembly comprising a pair of airfoil configurations mounted on a boom, whose movements are controlled by creating aerodynamic forces in the vertical and horizontal directions by deflecting the airfoils with respect to the flow.
U.S. Pat. No. 4,288,845 to Fisness et al. for "Aerial Refueling Receptacle Floodlights-Spoiler and Fuselage, Nose Mounted," relates to a floodlight illuminating system for use at night in combination with an aircraft having receptacle surfaces mounted on its nose section.
U.S. Pat. No. 4,158,885 to Neuberger, for "Guidance-Light Display Apparatus and Method for In-Flight Link-up of Two Aircraft," relates to a light system for mounting on a lead aircraft so as to be visible to a pilot of a trailing aircraft for guiding such pilot in flying the trailing aircraft into predetermined in-flight link-up position with respect to the lead aircraft. The apparatus comprises an array of guidance lights arranged on the body of the lead aircraft and sensor means for producing an electrical signal representing the instantaneous position and velocity of the trailing aircraft relative to the lead aircraft.
U.S. Pat. No. 4,072,283 to Weiland, for "Aerial Refueling Boom Articulation," relates to a flying refueling boom for an aerial tanker airplane, with a mechanism for moving the boom about different axes. The motion of the boom is obtained by deflecting a pair of aerodynamic surfaces mounted on it. The motion of the aerodynamic surfaces is controlled using a cable system that allows their deflection with respect to the air stream.
U.S. Pat. No. 4,025,193 to Pond et al., for "Apparatus Suitable for Use in Orienting Aircraft In-Flight for Refueling or Other Purposes," and U.S. Pat. No. 3,917,196 to Pond et al., for "Apparatus Suitable for Use in Orienting Aircraft Flight for Refueling or Other Purposes," both relate to a system capable of measuring both receiver aircraft and refueling boom locations relative to the tanker. This information is used either to automatically orient the two aircraft and the boom and nozzle or to generate displays suitable for both pilots in order to ease the refueling process.
U.S. Pat. No. 3,285,544 to Chope et al. for "Mid-Air Refueling System," relates to a system in which a nuclear radiation source is mounted on the probe of the receiving aircraft and a directional sensitive detector is mounted on the tanker, enabling the measurement of the relative elevation and azimuth of the drogue to the probe. The above measurements are used mainly to generate displays for the pilots of the aircraft for easier engagement, although the possibility of providing drogue-steering capability by means of an aerodynamic rigid rudder and stabilizer attached to the drogue is mentioned.